Technical Field
This disclosure relates to fan blade assemblies for gas turbine engines. More specifically, this disclosure relates to the use of a spinner, or one or more components of the nose cone assembly, for electrically grounding fan blades, which have the potential to build up a static electric charge.
Description of the Related Art
Gas turbine engines are known, and typically include a fan delivering air to a compressor section. In the compressor section, the air is compressed and then delivered to a combustion section. The compressed air is mixed with fuel and burned in the combustion section. Products of this combustion pass downstream to drive a turbine section, which in turn drives the compressor section.
The fan blades are subject to a large volume of air moving across an airfoil, which can result in a significant build-up of static electric charge. Conventionally, the fan blades are formed of a conductive metal, such as aluminum or titanium that is grounded to the metallic rotor or hub to which the fan blades are mounted. As the grounding is provided by the metallic rotor, the static electrical charge dissipates. However, aluminum fan blades may be covered with a polyurethane coating and/or fabric wear pads to protect the aluminum from erosion. These materials have insulation qualities, which interfere with the grounding of the fan blades to the rotor. As a result, static charges can build up on coated aluminum fan blades, thereby leading to galvanic corrosion.
Recently, fan blades have become larger. One factor driving the larger fan blades is the use of a gear reduction between a turbine driven spool, which drives the fan blades and the low-pressure compressor. The gear reduction allows a single turbine to drive both the low compressor and the fan, but at different speeds.
As the size of fan blades has increased, their weight has also increased, which adversely effects fuel efficiency. As a result, fan blade designs are being modified to reduce the weight of the fan blades. One such modification is to change the material used to fabricate the fan blades from titanium alloys and aluminum alloys to lighter materials, including, but not limited to composite materials. However, like titanium and aluminum, fan blades made from composite materials also have the ability to build up static charges. Further, a galvanic potential can develop from the use of multiple materials. Thus, fan blades made from a more than one material, e.g., a metallic body with a composite sheath, are prone to the development of a static charge buildup and therefore galvanic corrosion. Thus, static charge buildup on composite fan blades, metallic fan blades or fan blades made from multiple materials can cause galvanic corrosion.
To address this problem, grounding tabs may be installed that are physically connected to each fan blade, typically with an adhesive. The grounding tabs directly engage a component that is in contact with the rotor or the rotor itself thereby providing an electrical connection between the fan blade and the rotor, which serves to ground the fan blades.
However, as noted above, the grounding tabs are bonded to each fan blade. Not only does the use of grounding tabs add additional components and manufacturing steps to the fan blade assembly, the bonding between the grounding tabs and the fan blades can create gaps between the tabs and the fan blades, thereby making the grounding tabs ineffective as well as permitting moisture to penetrate between the grounding tabs and the fan blades.
Thus, improved methods and designs are needed for providing grounding for fan blades in general and, more specifically, for fan blades of gas turbine engines.